Gate-to-gate isolation for stacked transistor architecture via non-selective dielectric deposition structure

ABSTRACT

An integrated circuit structure having a stacked transistor architecture includes a first semiconductor body (e.g., set of one or more nanoribbons) and a second semiconductor body (e.g., set of one or more nanoribbons) above the first semiconductor body. The first and second semiconductor bodies are part of the same fin structure. The distance between an upper surface of the first semiconductor body and a lower surface of the second semiconductor body is 60 nm or less. A first gate structure is on the first semiconductor body, and a second gate structure is on the second semiconductor body. An isolation structure that includes a dielectric material is between the first and second gate structures, and on the first gate structure. In addition, at least a portion of the second gate structure is on a central portion of the isolation structure and between first and second end portions of the isolation structure.

FIELD OF THE DISCLOSURE

The present disclosure relates to integrated circuits, and moreparticularly, to stacked transistors.

BACKGROUND

Integrated circuitry continues to scale to smaller feature dimensionsand higher transistor densities. A more recent development with respectto increasing transistor density is generally referred to asthree-dimensional (3D) integration, which expands transistor density byexploiting the z-dimension (build upwards rather than laterally outwardsin the x- and y-dimensions). Some such 3D integrated circuits are formedutilizing a technique known as layer transfer. Such layer transfer mayinclude, for instance, bond and hydrogen-based or hydrogen/helium basedcleave techniques. Other 3D integrated circuits are formed by separatelyforming transistors on two distinct wafers (sometimes referred to ashost and donor wafers or substrates) and then bonding those two waferstogether via an oxide bonding layer, followed by chemical-mechanicalpolish (CMP) operations to remove excess wafer. Still other 3Dintegrated circuits are achieved by forming transistors on upper andlower regions of the same fin structure. In any such cases, such 3Dintegration schemes provide a stacked transistor architecture and giverise to a number of non-trivial issues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates a cross-section view of an integrated circuitstructure including a stacked transistor configuration havinggate-to-gate isolation provided by a non-selective deposition structure,in accordance with an embodiment of the present disclosure.

FIG. 1 b illustrates a cross-section view of a non-selective depositionstructure, in accordance with an embodiment of the present disclosure.

FIGS. 2-12 b are cross-sectional views that collectively illustrate anexample process for forming an integrated circuit structure including astacked transistor configuration having gate-to-gate isolation providedby a non-selective deposition structure, in accordance with someembodiments of the present disclosure.

FIG. 13 illustrates a methodology for providing gate-to-gate isolationby a non-selective deposition structure, in accordance with someembodiments of the present disclosure.

FIG. 14 illustrates a computing system implemented with one or moreintegrated circuit structures configured in accordance with anembodiment of the present disclosure.

As will be appreciated, the figures are not necessarily drawn to scaleor intended to limit the present disclosure to the specificconfigurations shown. For instance, while some figures generallyindicate perfectly straight lines, right angles, and smooth surfaces, anactual implementation of an integrated circuit structure may have lessthan perfect straight lines, right angles, and some features may havesurface topology or otherwise be non-smooth, given real worldlimitations of the processing equipment and techniques used. Likewise,while the thickness of a given first layer may appear to be similar inthickness to a second layer, in actuality that first layer may be muchthinner or thicker than the second layer; same goes for other layer orfeature dimensions.

DETAILED DESCRIPTION

A stacked transistor architecture is disclosed that employs a common finstructure that includes lower transistor and upper transistor portions.Although the techniques can be used with any number of transistorconfigurations, they are particularly useful with nanoribbon transistorconfigurations, due to the various challenging aspect ratiosattributable to the pancake-like nature of nanoribbons. One exampleembodiment provides an integrated circuit structure having a stackedtransistor architecture includes a first semiconductor body (e.g., firstset of one or more nanoribbons, or a first fin portion) and a secondsemiconductor body (e.g., second set of one or more nanoribbons, or asecond fin portion) above the first semiconductor body. The first andsecond semiconductor bodies are part of the same fin structure. Thedistance between an upper surface of the first semiconductor body and alower surface of the second semiconductor body is in the range of, forexample, 15 to 50 nanometers (nm). A first gate structure is on thefirst semiconductor body, and a second gate structure is on the secondsemiconductor body. An isolation structure that includes a dielectricmaterial is between the first and second gate structures, and is on thefirst gate structure. The isolation structure includes a first endportion, a second end portion, and a central portion between the firstand second end portions. The first and second end portions extend awayfrom the central portion toward the second gate structure, such that atleast a portion of the second gate structure is on the central portionof the isolation structure and between the first and second end portionsof the isolation structure. In an embodiment, the isolation structure isformed via a non-selective deposition process such as atomic layerdeposition (ALD), wherein a mask is used during removal of excessdielectric material that results from the non-selective deposition. Uponremoval of the mask, the isolation structure having the first and secondend portions along with the central portion remains. Numerousconfigurations will be apparent in light of this disclosure.

General Overview

As previously noted above, stacked transistor configurations give riseto a number of non-trivial issues. For instance, integrated circuitsemploying stacked complementary metal oxide semiconductor (CMOS)architecture may use vertical isolation between p-type MOS (PMOS) andn-type MOS (NMOS) metal gates. In a more general sense, a stackedtransistor architecture may call for vertical isolation between upperand lower metal gate structures. One possible solution for providingsuch isolation can be carried out during the gate forming process andinvolves first forming the lower gate structure, followed by depositinga dielectric material to fill up the remaining gate trench and thenrecessing it using an isotropic etch to leave an isolation layer behind.The upper gate structure can then be formed on that isolation layer, andthe upper channel region. Such solutions rely on there being arelatively large distance between the upper and lower channel regions(e.g., greater than 50 nm, such as 75 to 125 nm, or more). However, withcontinued scaling, there will be a very narrow margin/space budgetavailable between the upper and lower channel regions (e.g., 50 nm orless). To this end, if there is inadequate margin/space budget betweenthe top of the lower gate structure and the bottommost surface of theupper channel region, the isolation layer tends to take on a profilethat is conformal to the isotropic recess etch, rather than the topsurface of the lower gate structure. In particular, the isolation layerexhibits a peak under the lowest surface of the upper channel region.The closer the top of the isolation layer is to the lowest surface ofthe upper channel region, the more pronounced the peak ornon-conformality of the isolation layer. Likewise, the longer and/orwider the lowest surface of the upper channel region, the morepronounced the peak or non-conformality of the isolation layer. This isparticularly problematic for nanoribbon channel regions, which tend tobe relatively thin in the y-dimension but relatively long in thex-dimension and/or relatively wide in the z-dimension. In any case, suchnon-conformality of the isolation layer tends to decrease the thicknessof the gate electrode near the central portion of the lowermostnanoribbon or portion of the upper channel region.

Thus, techniques are disclosed for providing a conformal dielectric filmto provide electrical isolation between upper and lower gate structuresin a stacked transistor architecture. The dielectric film is formed bynon-selective deposition and is conformal to the underlying gatestructure topography. In addition, the dielectric film includes a firstend portion, a second end portion, and a central portion between thefirst and second end portions. The first and second end portions extendaway from the central portion toward the second gate structure, suchthat at least a portion of the second gate structure is on the centralportion of the dielectric film and between the first and second endportions of the dielectric film. In an embodiment, the dielectric filmis formed via a non-selective deposition process such as ALD, wherein amask is used during removal of excess dielectric film deposited on otherareas with the gate trench or elsewhere on the integrated circuitstructure being formed. Upon removal of the mask, the top surface of thecentral portion of dielectric film is substantially flat, while thefirst and second end portions extends toward the second gate structure.The central portion of the dielectric film therefore does not extendinto or otherwise meaningfully impact the shape or thickness of theupper gate structure. Other example embodiments may have some topologyin the central portion of the dielectric film, which may be okay in somecases. Although the techniques can be used with any number of transistorconfigurations, they are particularly useful with nanoribbon transistorconfigurations, due to the various challenging aspect ratiosattributable to the pancake-like nature of nanoribbons. In such cases,the gate structure wraps around the nanoribbon(s). The techniques mayalso be used, for example, with tri-gate and double-gate transistorconfigurations, where the gate structure is on both sides of asemiconductor fin (double-gate) or both sides and the top of the fin(tri-gate). In a more general sense, the techniques can be used in anystacked transistor configurations where there is a relatively smalldistance between the lower and upper semiconductor bodies that make upthe lower and upper channel regions, respectively. Numerousconfigurations will be apparent in light of this disclosure.

One example embodiment provides an integrated circuit structure thatincludes a first set of one or more nanoribbons and a second set of oneor more nanoribbons above the first set. The first and second sets ofnanoribbons are part of the same multilayer fin structure. The distancebetween the upper surface of the uppermost most nanoribbon of the firstset and the lower surface of the lowermost nanoribbon of the second setis 50 nm or less (e.g., 15 to 50 nm). A first gate structure wrapsarounds the first set of one or more nanoribbons, and a second gatestructure wraps around the second set of one or more nanoribbons. Notethat a portion of each of the first and second gate structures occupiesthe space between the upper surface of the uppermost most nanoribbon ofthe first set and the lower surface of the lowermost nanoribbon of thesecond set. An isolation structure is between the first and second gatestructures. The isolation structure includes a dielectric material(e.g., oxide, nitride, carbide, or a combination thereof) and is on atop surface of the first gate structure. The isolation structureincludes a central portion that extends laterally between first andsecond end portions. The first and second end portions extend away fromthe central portion toward the second gate structure, such that at leasta portion of the second gate structure is on the central portion of theisolation structure and between the first and second end portions of theisolation structure. The central portion of the isolation structure hasa thickness between the first and second gate structures that can varyfrom one embodiment to the next, but in some example cases is in therange of 1 to 5 nm. In some embodiments, the thickness of the centralportion is relatively consistent and varies less than 1 nm (e.g., suchas less than 8 angstroms, or less than 5 angstroms). The distance thatthe first and second end portions extend away from the central portioncan also vary from one embodiment to the next, but in some example casesis in the range of 4 to 10 nm.

The dielectric material of the isolation structure can vary from oneembodiment to the next, but in some example cases includes silicon, andone or more of oxygen, carbon, and nitrogen. Some specific examples forthe dielectric material of the isolation structure include siliconoxide, silicon carbide, silicon nitride, silicon oxycarbide, siliconoxynitride, or silicon oxycarbonitride. In a more general sense, thedielectric material of the isolation structure can be any dielectricfilm that provides a desired degree of gate-to-gate isolation.

The first gate structure includes a first gate electrode, and a firstgate dielectric between the first gate electrode and the first set ofone or more nanoribbons. Likewise, the second gate structure includes asecond gate electrode and a second gate dielectric between the secondgate electrode and the second set of one or more nanoribbons. The gatedielectrics can include, for example, a high-k dielectric (e.g., hafniumoxide) and may further include an underlying standard oxide (e.g., oxidenative to the nanoribbon material, such as silicon dioxide). The gateelectrodes can include a workfunction metal (e.g., titanium nitride forPMOS, or titanium aluminum carbide for NMOS) and a plug metal (e.g.,tungsten). A conformal gate spacer (e.g., silicon oxycarbonitride) maybe provided to either side of the gate stack (gate dielectric andelectrode), and in some example embodiments may also deposit on, and beleft on, sides of the fin structure in the source and drain regions andthus operate to constrain growth of epitaxial source and drain regions.

The integrated circuit structure may further include a first sourceregion and a first drain region, each adjacent to the first set of oneor more nanoribbons. Similarly, a second source region and a seconddrain region are adjacent to the second set of one or more nanoribbons.In this particular embodiment, the first and second source and drainregions are formed by an etch and replace process (also referred to asan epitaxial source and drain process), and comprise any number of dopedsemiconductor material (e.g., group IV such as silicon, germanium, orsilicon germanium, or group III-V semiconductors such as indium galliumarsenide). In one example case, the first source and drain regionsinclude a p-type dopant (e.g., boron doped silicon germanium, SiGe), andthe second source and drain regions include an n-type dopant (e.g.,phosphorus-doped silicon). In other embodiments, the first and secondsource and drain regions can be implantation-doped portions of the finstructure.

Another example embodiment provides a method of forming an integratedcircuit structure including a stacked transistor architecture with adielectric isolation layer between top and bottom gate structures. Themethod can be carried out, for example, as part of a gate-last processflow (although gate-first processes may also benefit from the techniquesprovided herein, as will be appreciated). In one such case, the methodincludes removing dummy gate material to expose upper and lower channelregions of the stacked transistor architecture, the upper and lowerchannel regions being part of a same multilayer fin structure. With thechannel regions now exposed, the method continues with releasing, via aselective etch process, a first nanoribbon of the lower channel regionand a second nanoribbon of the upper channel region. This releasing mayinclude, for instance, a selective etch that removes SiGe layers of analternating silicon-SiGe multilayer fin structure to release siliconnanoribbons, or a selective etch that removes the silicon layers of themultilayer fin structure to release SiGe nanoribbons. The methodcontinues with forming a first gate structure around each of the firstand second nanoribbons of the lower and upper channel regions,respectively, and then recessing that first gate structure to re-exposethe upper channel region, including the second nanoribbon. The methodcontinues with non-selectively and conformally depositing an isolationlayer on a top surface of the first gate structure. The method continueswith depositing a mask material (e.g., carbon hardmask) into the gatetrench, and then recessing that mask material to provide a relativelythin mask layer (e.g., 2-12 nm) over the isolation layer on the firstgate structure. The method then continues with removing the unmaskedportion of the isolation layer, and then removing the mask. The methodcontinues with forming a second gate structure around the secondnanoribbon of the upper channel region, the second gate structure on atop surface of the isolation structure. The dielectric material of theisolation layer may include, for example, silicon, and one or more ofoxygen, carbon, and nitrogen. In some embodiments, the distance from atop surface of the first nanoribbon to a bottom surface of the secondnanoribbon is in the range of 15 to 50 nm. In some embodiments, acentral portion of the isolation layer that extends laterally betweenfirst and second end portions has a relatively consistent thicknessbetween the first and second gate structures that varies less than 1 nm(e.g., less than 5 angstroms), the thickness being in the range of 1 to5 nm. The first and second end portions extend upward toward the secondgate structure, such as that at least a portion of the second gatestructure is between those first and second end portions. The first andsecond end portions provide evidence that a mask was used in the removalof excess isolation layer. Numerous variations will be apparent.

The method may further include forming a first source region and a firstdrain region, each adjacent to the first nanoribbon, and forming asecond source region and a second drain region, each adjacent to thesecond nanoribbon. Contacts for any of the gate structures, sourceregions, and drain regions can then be formed (e.g., frontside and/orbackside contact processing). Note, not all gate structures, sourceregions, and drain regions need to be contacted. Further note that notall upper and lower gate structures need to be separated by an isolationstructure; rather, some upper and lower gate structure pairs may beelectrically shorted to one another (with a conductive structure, ratherthan an isolation structure).

According to one example embodiment, the method provides a stacked CMOSstructure with a non-selectively deposited dielectric layer thatprovides electrical isolation between the gate structures of upper(e.g., NMOS) and lower (e.g., PMOS) nanoribbon transistors. Thedielectric layer is non-selective in that dielectric film (e.g., such assilicon oxycarbide) deposits on all exposed surfaces, and not just onthe top surface of the lower gate structure, and a subsequent maskingand etch process provides a dielectric film having bowl-shaped oru-shaped profile, according to some embodiments of the presentdisclosure. Use of the techniques provided herein will be apparent, forexample, via transmission electron microscopy (TEM) or high-resolutionscanning electron microscopy (SEM) imaging tools, which will revealplacement of a dielectric structure in a relatively narrow space betweenupper and lower channel regions, the dielectric structure having acentral portion that extends laterally between first and second endportions that both extend upward or otherwise away from the laterallyextending central portion, so as to provide a bowl-like profile.

Note that the top and bottom channel regions of the fin structure may beconfigured the same or differently, with respect to shape and/orsemiconductor materials, and may further include fin-based channelregions, nanowire-based channel regions, or nanoribbon-based channelregions. For instance, in one example, the lower channel region of thefin structure can be a fin portion of the fin structure and the upperchannel region can include one or more nanoribbons or nanowires includedin the fin structure. In such cases, the nanoribbons or nanowires arereleased during gate processing by removing sacrificial material alsoincluded in the fin structure. In some such example cases, the lowerportion of the fin structure comprises, for instance, SiGe or germaniumsuitable for PMOS devices, and the wires or ribbons of the upper portionof the fin structure comprise a group III-V semiconductor material suchas indium gallium arsenide, indium arsenide, or gallium antimonidesuitable for NMOS devices. In another example embodiment, the lowerchannel region is configured with a first fin portion of the finstructure comprising a first semiconductor material (e.g., SiGe), andthe upper channel region is configured with a second fin portion of thefin structure comprising a second semiconductor material (e.g., silicon)that is compositionally different from the first semiconductor material.Numerous variations and permutations will be apparent.

Materials that are “compositionally different” or “compositionallydistinct” as used herein refers to two materials that have differentchemical compositions. This compositional difference may be, forinstance, by virtue of an element that is in one material but not theother (e.g., SiGe is compositionally different than silicon), or by wayof one material having all the same elements as a second material but atleast one of those elements is intentionally provided at a differentconcentration in one material relative to the other material (e.g., SiGehaving 70 atomic percent germanium is compositionally different thanfrom SiGe having 25 atomic percent germanium). In addition to suchchemical composition diversity, the materials may also have distinctdopants (e.g., gallium and magnesium) or the same dopants but atdiffering concentrations. In still other embodiments, compositionallydistinct materials may further refer to two materials that havedifferent crystallographic orientations. For instance, (110) silicon iscompositionally distinct or different from (100) silicon. Creating astack of different orientations could be accomplished, for instance,with blanket wafer layer transfer.

Architecture

FIG. 1 a illustrates a cross-section view of an integrated circuitstructure including a stacked transistor configuration havinggate-to-gate isolation via a non-selective deposition structure, inaccordance with an embodiment of the present disclosure. The stackedtransistor configuration includes upper devices and lower devices,formed on the same fin structure. As can be seen, the cross-section istaken parallel to, and through, the fin structure, such that thechannel, source, and drain regions are shown. This particularcross-section includes three channel regions along with a source regionand a drain region, but any number of channel regions and correspondingsource and drain regions can be included, as will be appreciated.Further note that all transistors shown in this example are contacted,but other examples may include dummy devices or devices that are notconnected into the overall circuit. The semiconductor bodies 101 aincluded in the channel regions of the upper and lower transistors canvary in form, but in this example embodiment are in the form ofnanoribbons. In particular, the channel regions of the lower devices inthis example case each include a first set of four nanoribbons 101 a,and the channel regions of the upper devices each include a second setof four nanoribbons 101 a above the corresponding first set. Otherexamples may include fewer nanoribbons 101 a per channel region (e.g.,one or two), or more nanoribbons 101 a per channel region (e.g., five orsix). Still other embodiments may include other channel configurations,such as one or more nanowires or a fin or other semiconductor body,including both planar and nonplanar topologies. To this end, the presentdisclosure is not intended to be limited to any particular channelconfiguration or topology; rather the techniques provided herein can beused in any stacked transistor architecture where there is a relativelytight space budget between upper and lower gated channel regions and itis desired to have an isolation structure between those gated channelregions.

With further reference to FIG. 1 a, the lower device region includes asource region 109 and a drain region 110, each adjacent to a gatedchannel region on either side. Other embodiments may not have gatedchannel regions to each side, such as the example case where only thechannel region between source region 109 and drain region 110 ispresent. As can be further seen in this example, each of gate structures116-118 wraps around each of the nanoribbons 101 a in the correspondingchannel region. Gate spacer 105 c isolates gate structures 116-118 fromcontacting source region 109 and drain region 110. In other embodiments,there may be other insulator layers (e.g., interlayer dielectric) thatprevent such contact, whether in addition to gate spacer 105 c, or inplace of gate spacer 105 c. In addition, contacts 129 provide backsidecontact to respective gate structures 116-118, and contacts 131 providebackside contact to source region 109 and drain region 110. As can befurther scene, dielectric 127 prevents contacts 129 from contactingcontacts 131.

The upper device region includes a source region 113 and a drain region114, each with a gated channel region to either side. Again, otherembodiments may not have gated channel regions to each side, such as theexample case where only the channel region between source region 113 anddrain region 114 is present. As can be further seen in this example,each of gate structures 122-124 wraps around each of the nanoribbons 101a in the corresponding channel region. Gate spacer 105 c isolates gatestructures 122-124 from contacting source region 113 and drain region114. In other embodiments, there may be other insulator layers (e.g.,interlayer dielectric) that prevent such contact, whether in addition togate spacer 105 c, or in place of gate spacer 105 c. In addition,contacts 125 provide frontside contact to respective gate structures122-124, and contacts 131 provide frontside contact to source region 113and drain region 114. As can be further seen, dielectric 112 preventscontacts 125 from contacting contacts 115. In some embodiments, lowerand/or upper interconnect structures may be present, to further routesignals to and/or from contacts 115, 125, 129, 131. Any number ofsuitable interconnects schemes can be used.

As can further be seen in FIG. 1 a, isolation structure 121 preventsgate structures 116-118 from contacting gate structures 122-124,respectively. In particular, isolation structure 121 is between upperand lower gate structures and includes dielectric material, wherein theisolation structure 121 is on and a top surface of the underlying gatestructure, and a bottom surface of the upper gate structure is on a topsurface of the isolation structure 121. Note how at least a portion ofthe upper gate structure is laterally between first and second upwardlyextending end portions of the isolation structure 121. As can be furtherseen, isolation structure 111 prevents source region 109 from contactingsource region 113, and prevents drain region 110 from contacting drainregion 114.

As previously explained above, the geometry and spacing in the channelregions where isolation structure 121 is formed are such that, ifstandard processing techniques are used, isolation structure 121 issusceptible to having a non-flat upper surface in its central portion.Note that isolation structure 111 is less susceptible to such issues, asstandard epitaxial source and drain processing does not implicate thenarrow margin/space budget encountered during gate processing, largelybecause channel material remains in the gate trench so that the finalgate structure can be formed thereon, while material in the source anddrain regions can be completely removed and replaced.

In more detail, and with reference to FIG. 1 b, the distance d4 betweenthe upper surface of the first (lower) semiconductor body 101 a (e.g.,uppermost nanoribbon in lower channel region) and the lower surface ofthe second (upper) semiconductor body 101 a (e.g., bottommost nanoribbonin upper channel region) is in the range of 15 to 50 nm, according to anembodiment. Other embodiments may have different size constraints (e.g.,15 to 40 nm, 15 to 30 nm, 15 to 20 nm, 10 to 20 nm, or 10 to 60 nm). Inany such cases, that relatively small space has to accommodate not onlyisolation structure 121 but also the top portion of the lower gatestructure 117 and the bottom portion of the upper gate structure 123.Further recall that it is desirable to have the upper and lower gatestructures have consistent thicknesses, within a given channel region.To this end, a non-selectively deposited isolation structure 121 asprovided herein includes a central portion that extends laterallybetween first and second end portions, the central portion having arelatively consistent thickness between gate structures 117 and 123,such as the case where that thickness varies less than 1 nm. Thethickness of the central portion of isolation structure 121 is indicatedby distance dl in FIG. 1 b. In some embodiments, the largest thicknessof the central portion of isolation structure 121 between gatestructures 117 and 123 is within 1-8 angstroms of the smallest thicknessof the central portion of isolation structure 121 between gatestructures 117 and 123, with the average thickness (d1) of the centralportion of isolation structure 121 being in the range of, for example, 1to 5 nm. The first and second end portions extend away from the centralportion for a distance d2, which can vary depending on the maskthickness as will be explained in turn, but in some cases is in therange of 2 to 12 nm (e.g., 5-10 nm). Given the conformal nature ofisolation structure 121, the thickness of the upwardly extending firstand second end portions is about the same as the thickness of thecentral portion, as indicated by distance d1. So, in an example case,assume that: distance d4 is about 50 nm; distance dl is about 5 nm; anddistance d2 is about 5 nm; then distance d3 is about 10 nm. In such anexample, this would leave over 22 nm of thickness for each of the uppergate structure 123 and lower gate structure 117, with respect to thelaterally extending central portion of isolation structure 121. It isbelieved that the impact on gate structure dimension caused by the firstand second end portions of isolation structure 121 is less impactfulthan a comparable variance in thickness of the central portion ofisolation structure 121. Thus, the space allocated for gate structure ismeasured with respect to the central portion of isolation structure 121,rather than the end portions. Table 1 shows some examples includingthicknesses of the features between the upper and lower nanoribbons 101a. Other embodiments may have different dimensions.

TABLE 1 Example Dimensions Upper Lower Gate Gate Gate d4 d1 d2 d3Dielectric Electrode Electrode 50 nm 5 nm 5 nm 10 nm 5 nm 20 nm 20 nm 50nm 4 nm 5 nm 9 nm 4 nm 21 nm 21 nm 50 nm 3 nm 5 nm 8 nm 4 nm 21 nm 22 nm50 nm 2 nm 4 nm 6 nm 3 nm 23 nm 22 nm 50 nm 1 nm 1 nm 2 nm 2 nm 23 nm 24nm 50 nm 1 nm 1 nm 2 nm 1 nm 24 nm 24 nm 40 nm 5 nm 5 nm 10 nm 5 nm 15nm 15 nm 40 nm 4 nm 5 nm 9 nm 4 nm 16 nm 16 nm 40 nm 3 nm 5 nm 8 nm 4 nm16 nm 17 nm 40 nm 2 nm 4 nm 6 nm 3 nm 18 nm 17 nm 40 nm 1 nm 1 nm 2 nm 2nm 18 nm 19 nm 40 nm 1 nm 1 nm 2 nm 1 nm 19 nm 19 nm 35 nm 5 nm 5 nm 10nm 4 nm 13 nm 13 nm 35 nm 2 nm 5 nm 7 nm 3 nm 15 nm 15 nm 35 nm 2 nm 5nm 7 nm 2 nm 16 nm 15 nm 35 nm 2 nm 5 nm 7 nm 1 nm 16 nm 16 nm 30 nm 5nm 5 nm 10 nm 3 nm 11 nm 11 nm 30 nm 3 nm 4 nm 7 nm 3 nm 12 nm 12 nm 30nm 3 nm 4 nm 7 nm 2 nm 12 nm 13 nm 30 nm 3 nm 4 nm 7 nm 1 nm 13 nm 13 nm25 nm 3 nm 1 nm 3 nm 2 nm 10 nm 10 nm 25 nm 2 nm 1 nm 3 nm 2 nm 10 nm 11nm 25 nm 2 nm 1 nm 3 nm 1 nm 11 nm 11 nm 20 nm 2 nm 1 nm 3 nm 2 nm 8 nm8 nm 20 nm 2 nm 1 nm 3 nm 1 nm 9 nm 8 nm 15 nm 1 nm 1 nm 2 nm 2 nm 6 nm6 nm 15 nm 1 nm 1 nm 2 nm 1 nm 7 nm 6 nm

Note the example gate dielectric dimensions provided in Table 1 mayinclude one or more layers, such as a layer of silicon dioxide and alayer of high-k dielectric such as hafnium oxide or zirconium oxide.Recall that if the gate dielectric is only a single layer, thatdielectric may be regular or high-k.

With further reference to the example embodiment of FIG. 1 a, thedielectric material of the isolation structure 121 may include anynumber of dielectrics, including oxides, nitrides, carbides,oxynitrides, oxycarbides, and oxycarbonitrides. In some exampleembodiments, isolation structure 121 includes silicon, and one or moreof oxygen, carbon, and nitrogen (e.g., silicon oxycarbide, or siliconoxycarbonitride). The deposition can be timed, such that the thicknessof dielectric material deposited on the top surface of gate structures116-118 is within a desired range (e.g., 1 to 5 nm), and thus, nosubsequent etch to remove excess material in that location is needed,according to an embodiment. Other example embodiments may include apost-deposition isotropic etch to remove excess dielectric material inthat area on the top surface of gate structures 116-118, althoughconsideration can be given to the impact on variance in thickness of thecentral portion of the isolation structure, as previously explainedabove. The isolation structure 111 can be the same material as isolationstructure 121, but need not be. In one example embodiment, isolationstructure 111 is silicon dioxide, and isolation structure 121 is siliconoxycarbide.

Each of gate structures 116-118 and 122-124 can be formed via gate-firstor gate-last processing, and may include any number of suitable gatematerials and configurations. In an embodiment, each of the gatestructures 116-118 and 122-124 includes a gate electrode and a gatedielectric between the gate electrode and the correspondingsemiconductor body 101 a. Gate spacers 105 c may also be considered partof the gate structures, as will be appreciated in light of thisdisclosure. The gate spacers 105 c may be, for example, silicon nitrideor silicon dioxide or a carbon-doped oxide or an oxynitride or acarbon-doped oxynitride. The gate dielectrics (shown with thick boldedlines) may be any suitable gate dielectric material(s), such as silicondioxide or high-k gate dielectric materials. Examples of high-k gatedielectric materials include, for instance, hafnium oxide, hafniumsilicon oxide, lanthanum oxide, lanthanum aluminum oxide, zirconiumoxide, zirconium silicon oxide, tantalum oxide, titanium oxide, bariumstrontium titanium oxide, barium titanium oxide, strontium titaniumoxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, andlead zinc niobate. In some example embodiments, an annealing process maybe carried out to improve gate dielectric quality when a high-k materialis used. Further, the gate electrodes (shown with cross-hatching) maycomprise a wide range of suitable metals or metal alloys, such asaluminum, tungsten, cobalt, ruthenium, molybdenum, titanium, tantalum,copper, titanium nitride, or tantalum nitride, for example.

In some embodiments, the gate dielectrics and/or gate electrodes mayinclude a multilayer structure of two or more material layers orcomponents. For instance, in one such embodiment, the upper and/or lowergate dielectrics can be a bi-layer structure having a first dielectricmaterial (e.g., silicon dioxide) in contact with the correspondingchannel region 101 a and a second high-k dielectric material (e.g.,hafnium oxide) in contact with the first dielectric material. Likewise,the upper and/or lower gate electrodes may include a central metal plugportion (e.g., tungsten, cobalt, molybdenum, ruthenium) with one or moreouter workfunction layers (e.g., titanium nitride for PMOS workfunction,or an aluminum-containing alloy such as titanium aluminum carbide forNMOS workfunction) and/or barrier layers (e.g., tantalum nitride),and/or a resistance reducing cap layer (e.g., cobalt). In someembodiments, the gate dielectrics and/or gate electrodes may includeconcentration grading (increasing or decreasing) of one or morematerials therein.

Further note that the gate structures of the upper devices may be thesame as the gate structures of the lower devices, or different. In someexample embodiments, for instance, the gate dielectrics are the same forboth upper and lower gate structures, but the gate electrodes of theupper gate structures include an n-type workfunction metal suitable forNMOS devices (e.g., titanium aluminum nitride), while the gateelectrodes of the lower gate structures include a p-type work functionmetal suitable for PMOS devices (e.g., titanium nitride), or vice-versa.Likewise, the gate dielectric of the upper gate structures may becompositionally different from the gate dielectric of the lower gatestructures. In addition, or alternatively, the gate dielectric of theupper gate structures may have a first thickness, while the gatedielectric of the lower gate structures has a second thickness that isdifferent from the first thickness. For instance, the relatively thickergate dielectric may be used for a high voltage transistor device, whilethe relatively thinner gate dielectric may be used for a logictransistor device. Numerous gate structure configurations can be usedalong with the techniques provided herein, and the present disclosure isnot intended to be limited to any particular such configurations.

Likewise, numerous source and drain configurations can be used, and thepresent disclosure is not intended to be limited to any particular ones.In some example embodiments, the source and drain regions 109-110 and113-114 are epitaxial source and drain regions that are provided afterthe relevant portion of the fin or fin structure was isolated and etchedaway or otherwise removed. In other embodiments, the source/drainregions may be doped portions of the fin structure or substrate, ratherthan epi regions. In some embodiments using an etch and replace process,the epi source and drain regions 109-110 and 113-114 are faceted andovergrown from a trench within insulator material (e.g., shallow trenchisolation, or gate spacer 105 c that deposits on the sides of the finstructure in the source and drain locations), and the correspondingsource or drain contact structure lands on that faceted portion.Alternatively, in other embodiments, the faceted portion of epi sourceand drain regions can be removed (e.g., via chemical mechanicalplanarization, or CMP), and the corresponding source or drain contactstructure lands on that planarized portion.

The source and drain regions 109-110 and 113-114 can be any suitablesemiconductor material and may include any dopant scheme. For instance,source and drain regions 109-110 may be PMOS source and drain regionsthat include, for example, group IV semiconductor materials such assilicon, germanium, SiGe, germanium tin (GeSn), SiGe alloyed with carbon(SiGe:C). Example p-type dopants include boron, gallium, indium, andaluminum. Source and drain regions 113-114 can be NMOS source and drainregions that include, for example, silicon or group III-V semiconductormaterials such as two or more of indium, aluminum, arsenic, phosphorus,gallium, and antimony, with some example compounds including but notlimited to indium aluminum arsenide, indium arsenide phosphide, indiumgallium arsenide, indium gallium arsenide phosphide, gallium antimonide,gallium aluminum antimonide, indium gallium antimonide, or indiumgallium phosphide antimonide. In one specific embodiment, source anddrain regions 109-110 are boron-doped SiGe, and source and drain regions113-114 are phosphorus-doped silicon. In a more general sense, thesource and drain regions can be any semiconductor material suitable fora given application.

In some cases, the epi source and drain regions may include a multilayerstructure, such as a germanium cap on a SiGe body, or a germanium bodyand a carbon-containing SiGe spacer or liner between the correspondingchannel region and that germanium body. In any such cases, a portion ofthe epi source and drain regions may have a component that is graded inconcentration, such as a graded germanium concentration to facilitatelattice matching, or a graded dopant concentration to facilitate lowcontact resistance. Any number of source and drain configurations can beused as will be appreciated, and the present disclosure is not intendedto be limited to any particular such configurations.

The semiconductor bodies 101 a, which in this case are nanoribbons, canbe any number of semiconductor materials as well, such as group IVmaterial (e.g., silicon, germanium, or SiGe) or group III-V materials(e.g., indium gallium arsenide). In other embodiments, the semiconductorbodies 101 a may be fins on which the corresponding gate structures areformed to provide double-gate or tri-gate configurations (as opposed togate-all-around configurations with nanoribbons or wires). Thesemiconductor bodies 101 a may be lightly doped, or undoped, and may beshaped or sculpted during the gate formation process, according to someembodiments. In some cases, semiconductor bodies 101 a may be amultilayer structure, such as a SiGe body cladded with germanium, or asilicon body cladded with SiGe. Any number of channel configurations canbe used.

The contacts 115, 125, 129, and 131 can have any number ofconfigurations. In some example embodiments, the contacts 115, 125, 129,and 131 include a contact metal and a conductive liner or barrier layer,deposited in a contact trench formed in an insulator layer (e.g.,dielectric layers 112 and 127, such as silicon dioxide) over the sourceand drain regions. The liner can be, for example, tantalum or tantalumnitride, and metal can be any suitable plug/core material, such astungsten, aluminum, ruthenium, molybdenum, cobalt, titanium, copper, oralloys thereof. In some cases, the contacts 115, 125, 129, and 131 canbe optimized p-type and n-type similar to p-type and n-type gateelectrodes. For instance, according to some such embodiments, the linercan be titanium for NMOS source/drain contacts, or nickel or platinumfor PMOS source/drain contacts. In still other embodiments, the contacts115, 125, 129, and 131 may include resistance reducing materials (e.g.,nickel, platinum, nickel platinum, cobalt, titanium, germanium, nickel,gold, or alloys thereof such as germanium-gold alloy, or a multilayerstructure of titanium and titanium nitride all have good contactresistance), in addition to contact metal and any liner. Otherembodiments may be configured differently. In a more general sense, anynumber of suitable source/drain contact can be used in accordance withan embodiment of the present disclosure, as will be appreciated, and thepresent disclosure is not intended to be limited to any particular suchcontact configurations.

Methodology

FIG. 2 illustrates a cross-section view of a multilayer substrate 101that can be used to form a stacked transistor configuration havinggate-to-gate isolation via a non-selective deposition structure, inaccordance with an embodiment of the present disclosure. Distance d5 canbe set or otherwise adjusted to provide a desired distance between upperand lower channel regions, so as to leave sufficient room for formationof one or more gate-to-gate isolation structures, according to someembodiments (in such examples, note that distance d5 is the same asdistance d4 noted in FIG. 1 b ). Each layer can be formed by deposition(e.g., chemical vapor deposition, atomic vapor deposition, physicalvapor deposition) or layer transfer or other suitable process.Alternatively, substrate 101 can be purchased or otherwise preformed inadvance of the process (e.g., multilayer wafer).

As can be seen, the substrate 101 includes alternating layers ofmaterial 101 a and 101 b. Both layer materials can be semiconductormaterials, such as alternating layers of silicon (e.g., 101 a) and SiGe(e.g., 101 b), according to some embodiments. In other embodiments, onematerial can be a sacrificial dielectric material, such as alternatinglayers of silicon (e.g., 101 a) and silicon dioxide (e.g., 101 b). Instill other embodiments, substrate 101 may include alternating layers ofsilicon (e.g., 101 a) and SiGe (e.g., 101 b), and further include amiddle layer 101 c of an insulator material such as silicon dioxide. Inany such cases, the alternating materials making up layers 101 a and 101b (and 101 c, if present) can be selectively etched with respect to oneanother, so that a sacrificial one of the materials can be selectivelyetched away so as to liberate the other material to provide nanoribbonsor wires, according to some embodiments. In other embodiments, thesubstrate 101 may include a relatively thick top semiconductor layer 101a and a relatively thick bottom semiconductor layer 101 a separated by adielectric layer 101 b (or 101 c), which could be used to form upper andlower fin portions suitable for stacked double-gate transistors ortri-gate transistors.

The resulting stack as well as the individual layers can have any numberof thicknesses, and are not necessarily drawn to scale. For instance, insome such example embodiments, each of the layers 101 a and 101 b are inthe range of 5 to 100 nm thick, except the bottommost layer 101 a may bea relatively thicker layer or bulk substrate, and the middle layer 101 bhas a thickness d5 that can be varied to set the working distancebetween the upper and lower channel regions, such as 10 to 60 nm or 15to 50 nm or 15 to 40 nm or 15 to 30 nm, according to some embodiments(again, in such examples, note that distance d5 is the same as distanced4 of FIG. 1 b ). In a more general sense, each of the one or morelayers making up substrate 101 may be set to any suitable thickness aswill be appreciated.

FIG. 3 a shows the resulting structure after substrate 101 has beenpatterned and etched to form a number of multilayer fin structures, anda dummy gate structure 105 has been formed thereon, according to anembodiment. The cross-section is taken parallel to, and through, dummygate structure 105. As can be seen, four fin structures are shown, butany number of such fin structures can be made. The fin structure on thefar left shows an alternative fin configuration, where the bottomportion of the fin structure is configured for fin-based channel regionsand the top portion of the fin structure is configured withnanoribbon-based channel regions. An insulator layer 101 c (e.g.,silicon dioxide) is provided between the upper and lower portions. Suchan insulator layer 101 c may also be substituted for the mid-layer 101 bhaving the thickness of d5, in the example multilayer fins to the right.As will be discussed in turn, such a native insulator structure 101 c(native to the substrate) can be used to separate upper source and drainregions from lower source and drain regions, in cases where the uppersource and drain regions are provided by topside processing and thelower source and drain regions are provided by bottomside processing. Ifboth upper and lower source and drain regions are formed from the sameside (e.g., topside), then any such a native mid-layer would be etchedaway and replaced between lower and upper source/drain region formingprocesses. Numerous other configurations can be used, as will beappreciated. To this end, the present disclosure is not intended to belimited to nanoribbons or any particular fin structure, even though thefigures are primarily focused on nanoribbons. The techniques providedherein can be used with planar transistor technologies as well, as willbe appreciated in light of this disclosure.

The dummy gate structure 105 can be any standard or proprietary gatestructure. According to an embodiment, the dummy gate structure 105 isformed by a blanket deposition of the dummy gate material(s) followed bya masking and etch to remove the excess gate material(s), such that thedummy gate structure 105 only remains across the channel regions of thefins. The configuration of the dummy gate structure 105 can vary fromone embodiment to the next, but in some embodiments includes amorphoussilicon, and in still other embodiments such as best shown in FIG. 3 bincludes a dummy gate electrode 105 a (e.g., polysilicon), a dummy gatedielectric 105 b (e.g., an oxide of the channel material 101 a or 101b), and a gate spacer 105 c (e.g., silicon oxycarbonitride, or othermaterial that is etch selective with respect to other the dummy gatematerial or materials). Note that the cross-section of FIG. 3 b is takenperpendicular to, and through, the dummy gate structure 105, at dashedline 3 b-3 b indicated in FIG. 3 a. A gate cap may also be provided ontop of the dummy gate structure 105, to protect the dummy gate structureduring subsequent source and drain processing, and can be any number ofmaterials, such as silicon nitride. Once the dummy gate structure 105 isformed, dielectric 103 is deposited (e.g., CVD) and planarized down tothe top of the dummy gate structure (or gate cap) using a CMP process,as best shown in FIG. 3 c. Dielectric 103 can be any number ofdielectrics, such as those that have etch selectivity to gate spacers105 c. So, for instance, dielectric 103 can be an oxide such as silicondioxide, and spacers 105 c can be a nitride or carbide such as siliconnitride, silicon oxynitride, or silicon oxycarbonitride. Like FIG. 3 a,the cross-section of FIG. 3 c is taken parallel to dummy gate structure105, but through the portion of the fin structures where the source ordrain regions will be formed.

The dimensions of the dummy gate structure 105 can vary from oneembodiment to the next, as will be appreciated. In some example cases,the distance from the top of a given fin to the top of the dummy gatestructure 105 is in the range of 50 to 100 nm (e.g., 75 nm). The widthof the dummy gate structure 113 will also vary, depending on factorssuch as desired channel length and/or fin thickness (for non-planartransistors), but in some cases is in the range of 10 to 100 nm. Ifpresent, the thickness of the gate cap may be, for example, in the rangeof 20 to 100 nm (e.g., 30 to 75 nm). If present, a dummy gate dielectric105 b may have a thickness in the range of, for example, one or moremonolayers to 10 nm. The gate spacers 105 c, when present, can beconformally deposited and have any desired thickness, such as in therange of 3 to 40 nm. As will be explained in turn, the gate spacer 105 cmay be conformally deposited in a blanket fashion so as to also coverthe exposed sidewalls of fin portions where the source and drain regionswill be formed, and thus can subsequently be used as a guide in anepitaxial source and drain formation process.

FIG. 4 is the cross-sectional view of the structure of FIG. 3 c afterthe lower source or drain regions 109 and upper source or drain regions113 have been formed, along with isolation structure 111, in accordancewith an embodiment. Like FIG. 3 c, the cross-section of FIG. 4 is takenparallel to dummy gate structure 105, but through the portion of the finstructures where the source or drain regions are formed. As previouslyexplained, source or drain regions 109 and 113 can be formed using anystandard or proprietary source and drain processing method. In thisexample case, source or drain regions 117 and 119 are formed by an etchand replace process, where original fin material is etched away andreplaced via epitaxial deposition of the desired source and drainmaterials. As can be seen, gate spacer 105 c can be used as a guideduring the epitaxial growth of the source or drain regions 109 and 113,which constrains faceting of source or drain regions 109 and 113. Insome example embodiments, source or drain regions 109 are PMOS source ordrain regions (e.g., epitaxial SiGe doped with boron), and source ordrain regions 113 are NMOS source or drain regions (e.g., epitaxialsilicon doped with phosphorus), so as to provide complementary MOS(CMOS) logic or memory cells. The previous discussion with reference toexample source and drain materials, configurations and forming methodsis equally applicable here.

In this example embodiment, the source or drain regions 109 and 113 areformed from the topside of the structure using a sequential depositionand etch process such as: etch away the fin structure in both the upperand lower source/drain regions; epitaxially deposit source or drainregions 109 and etch away any excess deposition; deposit isolationstructure 111 and etch away any excess deposition; and epitaxiallydeposit source or drain regions 113 and etch away any excess deposition.In other embodiments, the upper source or drain regions 113 can beformed from the topside, while the lower source or drain regions 109 canbe formed from the backside after the bottommost substrate 101 a portionhas been removed. In such cases, isolation structure 111 can beprovisioned at an appropriate point in that processing, such as betweenetching away the portion of the fin structure in the upper source/drainregions and epitaxially depositing source or drain regions 113, orbetween etching away the portion of the fin structure in the lowersource/drain regions and epitaxially depositing source or drain regions109. In still other examples that utilize topside processing to formsource or drain regions 113 and bottomside processing to form source ordrain regions 109, isolation structure 111 can be built into orotherwise native the fin structure, such as 101 c which can be, forinstance, an oxide layer. In such cases, the etching away of the finstructure from topside and bottomside directions can be stopped once theisolation structure 111 is reached. The dielectric of isolationstructure 111 and dielectric 112 can be, for example, the samedielectric material as used for dielectric 103 (e.g., silicon dioxide),but need not be.

FIG. 5 is the cross-sectional view of the structure of FIG. 4 aftercontacts 115 have been formed over upper source or drain regions 113,dummy gate structure 105 has be removed, and nanoribbons 101 a have beenreleased by selectively etching away sacrificial material 101 b, inaccordance with an embodiment. Here, the cross-section is taken parallelto, and through, one of the fin structures, so as to show source,channel, and drain regions of upper and lower transistors. Note thesource and drain regions 109, 110, 113, and 114 are depicted in thisexample case with some faceting. Other embodiments may not include suchfaceting, or may include a higher degree of faceting. Contacts 115 canbe any suitable contact configuration, and the previous relevantdiscussion is equally applicable here. As also previously explained,that nanoribbon release process can be, for example, part of a gateforming process where the channel region is first exposed by removingany dummy gate materials (if a gate-last process is used), followed byan etch that is selective to the semiconductor 101 a and not thesacrificial material 101 b (i.e., the etch removes the sacrificialmaterial 101 b at a much higher rate than the semiconductor 101 amaterial). Note that the source or drain regions can be masked off orotherwise protected during this gate processing. Any number of selectiveetch schemes can be used, as will be appreciated. For instance, in oneexample embodiment, sacrificial material 101 b is silicon andsemiconductor material 101 a is germanium or SiGe, and etch chemistriessuch as aqueous hydroxide chemistries, including ammonium hydroxide andpotassium hydroxide, for example, may be utilized to selectively etchthe silicon 101 b but leave the germanium-containing nanowires ornanoribbons 101 a in place. In another example embodiment, sacrificialmaterial 101 b is germanium-containing material and semiconductormaterial 101 a is silicon, and etch chemistries such as carboxylicacid/nitric acid/hydrogen fluoride chemistry, and citric acid/nitricacid/hydrogen fluoride, for example, may be utilized to selectively etchthe germanium-containing material 101 b but leave the silicon 101 a inplace. Any number of material systems and selective etch schemes can beused, as will be appreciated.

FIG. 6 is the same cross-sectional view of the structure of FIG. 5 ,after lower gate structures 116-118 have been formed, in accordance withan embodiment. Standard gate structure deposition techniques can beused. As can be seen, each gate structure 116-118 includes a gatedielectric (shown with thick bolded lines) and a gate electrode (shownwith cross-hatching). In the example embodiment shown, the gatedielectric deposition is non-selective, in that the gate dielectric isdeposited on exposed surfaces within the gate trench. CVD or ALD can beused to provide the gate dielectric at a desired thickness, such as athickness in the range of, for example, one or more monolayers to 10 nm.In this embodiment, the gate dielectric is the same for both upper andlower gate structures, but it need not be. The gate electrode is thendeposited onto the gate dielectric. Note that the lower gate electrodematerial(s) will also be deposited onto the upper device region channelregions, as well as may the gate dielectric, which is okay as suchexcess gate materials can be subsequently etched back or otherwiseremoved via a subsequent etch process, as shown in FIG. 6 . A mask(e.g., carbon hardmask) may be used to protect the underlying lower gatestructure while etching away the excess gate materials to re-expose theupper channel region. Once the excess gate material is removed, the maskcan also be removed using a standard mask removal etch. The previousrelevant discussion with respect to gate dielectrics and gate electrodesis equally applicable here, as will be appreciated.

FIG. 7 is the same cross-sectional view of the structure of FIG. 6 ,after dielectric material that will ultimately provide isolationstructure 121, has been deposited, in accordance with an embodiment. Ascan be seen, the dielectric material is non-selectively deposited and isconformally applied to all exposed surfaces within the gate trench. ALDis used to deposit the dielectric material, according to an embodiment,although other embodiments may use other deposition techniques (e.g.,CVD). Note that smaller spaces, such as those between neighboringnanoribbons, may fill completely as the conformal dielectric growth onopposing surfaces meets in the middle of that smaller space to form aseam or grain boundary. The deposition can be timed, such that thethickness of dielectric material deposited on the top surface of gatestructures 116-118 is within a desired range (e.g., 1 to 5 nm), andthus, no subsequent etch to remove excess material in that location isneeded, according to an embodiment. Such timing will vary from oneembodiment to the next, but may be established theoretically and/orempirically, and in some example cases is in the range of 0.5 to 4minutes (e.g., about 60 to 120 seconds). Other example embodiments mayinclude a post-deposition isotropic etch to remove excess dielectricmaterial in that area on the top surface of gate structures 116-118,although consideration can be given to the impact on variance inthickness of the central portion of the isolation structure, aspreviously explained above.

As previously explained above, the dielectric material of isolationstructure 121 may include any number of dielectrics, including oxides,nitrides, carbides, oxynitrides, oxycarbides, and oxycarbonitrides. Insome example embodiments, isolation structure 121 includes silicon, andone or more of oxygen, carbon, and nitrogen (e.g., silicon dioxide,silicon oxycarbide, or silicon oxycarbonitride). In a more generalsense, the dielectric material can be any material that can beselectively etched with respect to the gate dielectric, gate spacer 105c, and any other exposed layers (e.g., barrier or liner layers).

FIG. 8 a is the same cross-sectional view of the structure of FIG. 7 ,after a mask 120 material has been deposited into the gate trench, inaccordance with an embodiment. Note that the deposition may completelyfill the trench, but it need not. The mask 120 can be, for example, acarbon hardmask or photoresist, in some embodiments. FIG. 8 b show theresulting structure after mask 120 has been etched to provide a desiredmask thickness. Note the final mask 120 occupies only a portion of thespace between the upper and lower channel regions. Although thethickness of the mask 120 can vary from one embodiment to the next, insome embodiments the thickness is in the range of 6 to 12 nm (e.g., 5 to10 nm). Further note that the thickness of mask 120 will largely dictatethe distance that the end portions of the final isolation structure 121extend away from the central portion of structure 121.

FIG. 9 is the same cross-sectional view of the structure of FIG. 8 ,after final isolation structures 121 have been formed above each of thelower gate structures, and after the mask 120 has been removed, inaccordance with an embodiment. With mask 120 in place, an isotropic etchcan be used to remove the excess dielectric material of isolationstructure 121, such that only the bowl-shaped or u-shaped portion of theisolation structure 121 that is protected by mask 120 remains As can beseen, the resulting isolation structures 121 each includes first andsecond end portions, and a central portion between those first andsecond end portions. Note how the thickness of mask 120 sets thedistance that the first and second end portion extend beyond the topsurface of the central portion. As can be further seen, the first andsecond end portions extend upward in this example case from the centralportion toward the corresponding upper gate structure (122-124), suchthat at least a portion of the upper gate structure will be on thecentral portion of the isolation structure 121 and between the first andsecond end portions of the isolation structure. In this manner, thecorresponding upper gate structures 122-124 will each effectively sitwithin the underlying isolation structure 121. Further note in thisexample that the first and second end portions do not contact the gatedielectric. Thus, there will be at least some portion of the gateelectrode between each uppermost end portion and the gate dielectricthereabove. Once the final isolation structure 121 is formed, the maskcan be removed using any suitable mask removal etch (e.g., plasma ashingetch).

FIG. 10 is the same cross-sectional view of the structure of FIG. 9 ,after upper gate structures 122-124 have been formed, in accordance withan embodiment. Again, standard gate structure deposition techniques canbe used. As can be seen, each gate structure 122-124 includes a gatedielectric (shown with thick bolded lines) and a gate electrode (shownwith cross-hatching). Note that the upper gate dielectric that depositedduring the lower gate structure processing may be etched away andreapplied, to improve quality of the upper gate dielectric. The gateelectrode is then deposited onto the gate dielectric. The previousrelevant discussion with respect to gate dielectrics and gate electrodesis equally applicable here, as will be appreciated. As previously noted,at least a portion of the upper gate structure is on the central portionof the isolation structure 121 and between the first and second endportions of the isolation structure, such that the corresponding uppergate structures 122-124 each effectively sit within the underlyingisolation structure 121.

FIG. 11 is the same cross-sectional view of the structure of FIG. 10 ,after gate contacts 125 have been formed, in accordance with anembodiment. Standard contact deposition techniques can be used. Notethat excess gate dielectric (thick bolded lines) can be removed via etchprocess, in some embodiments. The previous relevant discussion withrespect to contacts is equally applicable here, as will be appreciated.

FIG. 12 a is the same cross-sectional view of the structure of FIG. 11 ,after the structure has been rotated 180 degrees and the lower substrate101 a has been removed (e.g., CMP), and dielectric layer 127 has beendeposited, in accordance with an embodiment. Dielectric 127 can be, forexample, the same as dielectric 103 and 112. FIG. 12 b is the samecross-sectional view of the structure of FIG. 12 a, after dielectriclayer 127 has been patterned and contacts 129 and 131 are depositedtherein, in accordance with an embodiment. The previous relevantdiscussion with respect to contacts is equally applicable here, as willbe appreciated.

FIG. 13 illustrates a methodology for forming an integrated circuitstructure including a stacked transistor architecture with a dielectricisolation layer between top and bottom gate structures, in accordancewith some embodiments of the present disclosure. The method can be usedto form, for instance, gate isolation structures 121 such as those shownin the examples of FIGS. 1 a and 1 b, although other integrated circuitstructures may include such isolation structures as well.

The method includes removing 1302 dummy gate material to expose upperand lower channel regions of the stacked transistor architecture, theupper and lower channel regions being part of a same fin structure. Inthis example case, the fin structure is a multilayer fin structuresuitable for nanoribbons, although other embodiments may have adifferent fin structure as previously explained.

The method continues with releasing 1304, via a selective etch process,a first nanoribbon of the lower channel region and a second nanoribbonof the upper channel region. In some cases, the longest distance betweenthe top surface of the first nanoribbon and the bottom surface of thesecond nanoribbon is in the range of 10 to 60 nm, or 15 to 50 nm, or 15to 40 nm, or 15 to 30 nm, or 15 to 25 nm.

The method continues with forming 1306 a first gate structure aroundeach of the first and second nanoribbons of the lower and upper channelregions, respectively, and then recessing the first gate structure tore-expose the upper channel region, including the second nanoribbon. Themethod continues with non-selectively and conformally depositing 1308 anisolation structure on a top surface of the first gate structure. Themethod continues with depositing 1310 a mask on the isolation structure,and then recessing the mask to a thickness of, for example, 2 to 12 nm(e.g., 2 to 10 nm, or 5 to 10, or 4 to 8 nm). With the mask in place,the method continues with removing 1312 the unmasked portion of theisolation structure, and then removing 1314 the mask. The method furtherincludes forming 1316 a second gate structure around the secondnanoribbon of the upper channel region, the second gate structure alsoon a top surface of the isolation structure. In some embodiments, ALD isused to deposit both the gate dielectric and gate electrode materials,as well as the isolation structure.

The resulting isolation structure includes a first end portion, a secondend portion, and a central portion between the first and second endportions. The first and second end portions extend away from the centralportion toward the second gate structure, such that at least a portionof the second gate structure is on the central portion of the isolationstructure and between the first and second end portions of the isolationstructure. The central portion of the isolation structure has athickness between the first and second gate structures that can varyfrom one embodiment to the next, but in some example cases is in therange of 1 to 5 nm. In some embodiments, the thickness of the centralportion is relatively consistent and varies less than 1 nm (e.g., suchas less than 8 angstroms, or less than 5 angstroms). The distance thatthe first and second end portions extend away from the central portioncan also vary from one embodiment to the next (depending on the maskthickness), but in some example cases is in the range of 5 to 10 nm.

In some cases, forming the first gate structure at 1306 includesdepositing a first high-k gate dielectric and then depositing a firstgate electrode, and forming the second gate structure at 1306 includesdepositing a second high-k gate dielectric and then depositing a secondgate electrode. In some cases, prior to forming the first gate structureat 1306, the method includes depositing a passivation layer on thesecond nanoribbon of the upper channel region, to protect that upperchannel region from exposure to processing of the lower channel region.In some cases, the longest distance from a top surface of the firstnanoribbon to a bottom surface of the second nanoribbon is in the rangeof 15 to 50 nm. In some cases, the largest thickness of the isolationstructure central portion between the first and second gate structuresis within 10 angstroms of the smallest thickness of the isolationstructure central portion between the first and second gate structures,or within 8 angstroms, or within 6 angstroms, or within 4 angstroms. Theaverage thickness of the isolation structure central portion between thefirst and second gate structures may be, for instance, in the range of 1to 10 nm, or 1 to 8 nm, or 1 to 5 nm, or 1 to 4 nm, or 1 to 5 nm, or 1to 2 nm.

In some cases, the method includes forming a first source region and afirst drain region, each adjacent to the first nanoribbon, and forming asecond source region and a second drain region, each adjacent to thesecond nanoribbon. In some cases, the first source and drain regionscomprise one of a p-type or n-type dopant, and the second source anddrain regions comprise the other of the p-type or n-type dopant.

Computing System

FIG. 14 illustrates a computing system implemented with one or moreintegrated circuit structures configured in accordance with anembodiment of the present disclosure. As can be seen, the computingsystem 1400 houses a motherboard 1402. The motherboard 1402 may includea number of components, including but not limited to a processor 1404and at least one communication chip 1406 (two are shown in thisexample), each of which can be physically and electrically coupled tothe motherboard 1402, or otherwise integrated therein. As will beappreciated, the motherboard 1402 may be, for example, any printedcircuit board, whether a main board or a daughterboard mounted on a mainboard or the only board of system 1400, etc. Depending on itsapplications, computing system 1400 may include one or more othercomponents that may or may not be physically and electrically coupled tothe motherboard 1402. These other components may include, but are notlimited to, volatile memory (e.g., DRAM), non-volatile memory (e.g.,ROM), a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth). Any of the components included in computingsystem 1400 may include one or more integrated circuits configured witha stacked transistor configuration having gate-to-gate isolation, asvariously described herein. In some embodiments, multiple functions canbe integrated into one or more chips (e.g., for instance, note that thecommunication chip 1406 can be part of or otherwise integrated into theprocessor 1404).

The communication chip 1406 enables wireless communications for thetransfer of data to and from the computing system 1400. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 1406 may implementany of a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing system 1400 may include a plurality ofcommunication chips 1406. For instance, a first communication chip 1406may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 1406 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others. The processor 1404 of the computingsystem 1400 includes an integrated circuit die packaged within theprocessor 1404. In some example embodiments of the present disclosure,the integrated circuit die of the processor 1404 includes one or moreoccurrences of a non-selectively deposited gate-to-gate isolationstructures as variously provided herein. The term “processor” may referto any device or portion of a device that processes, for instance,electronic data from registers and/or memory to transform thatelectronic data into other electronic data that may be stored inregisters and/or memory.

The communication chip 1406 may also include an integrated circuit diepackaged within the communication chip 1406. In accordance with somesuch example embodiments, the integrated circuit die of thecommunication chip 1406 includes one or more occurrences of anon-selectively deposited gate-to-gate isolation structures as variouslyprovided herein. As will be appreciated in light of this disclosure,note that multi-standard wireless capability may be integrated directlyinto the processor 1404 (e.g., where functionality of any chips 1406 isintegrated into processor 1404, rather than having separatecommunication chips). Further note that processor 1404 may be a chip sethaving such wireless capability. In short, any number of processor 1404and/or communication chips 1006 can be used. Likewise, any one chip orchip set can have multiple functions integrated therein.

In various implementations, the computing system 1400 may be a laptop, anetbook, a notebook, a smartphone, a tablet, a personal digitalassistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer,a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the system 1400may be any other electronic device that processes data or employs one ormore non-selectively deposited gate-to-gate isolation structures asvariously provided herein. As will be appreciated in light of thisdisclosure, various embodiments of the present disclosure can be used toimprove performance on products fabricated at any process node (e.g., inthe micron range, or sub-micron and beyond) by allowing for the use ofvertically stacked transistors having any number of source/drainconfigurations and channel configurations, along with one or morenon-selectively deposited gate-to-gate isolation structures as variouslyprovided herein.

Further Example Embodiments

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent.

Example 1 includes an integrated circuit structure, comprising: a firstsemiconductor body; a second semiconductor body above the firstsemiconductor body, wherein the longest distance between an uppersurface of the first semiconductor body and a lower surface of thesecond semiconductor body is 50 nm or less, and wherein the first andsecond semiconductor bodies are part of a same fin structure; a firstgate structure on the first semiconductor body; a second gate structureon the second semiconductor body; and an isolation structure between thefirst and second gate structures and comprising dielectric material,wherein the isolation structure is on a top surface of the first gatestructure, the isolation structure including a central portion thatextends laterally between first and second end portions, the first andsecond end portions extending away from the central portion toward thesecond gate structure, such that at least a portion of the second gatestructure is on the central portion of the isolation structure andbetween the first and second end portions of the isolation structure.

Example 2 includes the subject matter of Example 1, wherein thedielectric material of the isolation structure includes silicon, and oneor more of oxygen, carbon, and nitrogen.

Example 3 includes the subject matter of Example 1 or 2, wherein thedielectric material of the isolation structure includes silicon, oxygen,and carbon.

Example 4 includes the subject matter of any one of Examples 1 through3, wherein the first gate structure includes a first gate electrode anda first gate dielectric between the first gate electrode and the firstsemiconductor body, and/or the second gate structure includes a secondgate electrode and a second gate dielectric between the second gateelectrode and the second semiconductor body.

Example 5 includes the subject matter of any one of Examples 1 through4, wherein the first semiconductor body includes a first nanoribbon, andthe first gate structure wraps around the nanoribbon, and wherein thesecond semiconductor body includes a second nanoribbon, and the secondgate structure wraps around the second nanoribbon, and wherein thelongest distance is a distance from a top surface of the firstnanoribbon to a bottom surface of the second nanoribbon and is in therange of 15 to 50 nm.

Example 6 includes the subject matter of any one of Examples 1 through5, wherein variation of the isolation structure central portionthickness between the first and second gate structures is less than 8angstroms.

Example 7 includes the subject matter of any one of Examples 1 through6, wherein variation of the isolation structure central portionthickness between the first and second gate structures is less than 6angstroms.

Example 8 includes the subject matter of any one of Examples 1 through7, wherein variation of the isolation structure central portionthickness between the first and second gate structures is less than 4angstroms.

Example 9 includes the subject matter of any one of Examples 1 through8, and further includes: a first source region and a first drain region,each adjacent to the first semiconductor body; and a second sourceregion and a second drain region, each adjacent to the secondsemiconductor body; wherein the first source and drain regions compriseone of a p-type or n-type dopant, and the second source and drainregions comprise the other of the p-type or n-type dopant.

Example 10 includes the subject matter of any one of Examples 1 through9, wherein the longest distance between the upper surface of the firstsemiconductor body and the lower surface of the second semiconductorbody is in the range of 15 to 40 nm.

Example 11 includes the subject matter of any one of Examples 1 through10, wherein the longest distance between the upper surface of the firstsemiconductor body and the lower surface of the second semiconductorbody is in the range of 15 to 30 nm.

Example 12 includes the subject matter of any one of Examples 1 through11, wherein the longest distance between the upper surface of the firstsemiconductor body and the lower surface of the second semiconductorbody is in the range of 15 to 20 nm.

Example 13 is a processor or memory comprising the integrated circuitstructure of any one of Examples 1 through 12.

Example 14 is an integrated circuit structure, comprising: a firstnanoribbon comprising a first semiconductor material; a secondnanoribbon above the first nanoribbon and comprising the firstsemiconductor material, wherein the distance between a top surface ofthe first nanoribbon and a bottom surface of the second nanoribbon is inthe range of 15 to 50 nm, and wherein the first and second nanoribbonsare part of a same multilayer fin structure; a first gate structurearound the first nanoribbon, the first gate structure including a firstgate electrode and a first high-k gate dielectric between the first gateelectrode and the first nanoribbon; a second gate structure around thesecond nanoribbon, the second gate structure including a second gateelectrode and a second high-k gate dielectric between the second gateelectrode and the second nanoribbon; and an isolation structure betweenthe first and second gate structures and comprising dielectric material,wherein the isolation structure is on a top surface of the first gatestructure, and a bottom surface of the second gate structure is on a topsurface of the isolation structure, and wherein the isolation structureincludes a central portion that extends laterally between first andsecond end portions, the first and second end portions extending awayfrom the central portion toward the second gate structure for a distanceof 2 to 12 nm, such that at least a portion of the second gate structureis on the central portion of the isolation structure and between thefirst and second end portions of the isolation structure.

Example 15 includes the subject matter of Example 14, wherein thedielectric material of the isolation structure includes silicon, oxygen,and carbon.

Example 16 includes the subject matter of Example 14 or 15, wherein alargest thickness of the isolation structure central portion between thefirst and second gate structures is within 10 angstroms of a smallestthickness of the isolation structure central portion between the firstand second gate structures.

Example 17 includes the subject matter of Example 16, wherein thelargest thickness of the isolation structure central portion between thefirst and second gate structures is within 6 angstroms of the smallestthickness of the isolation structure central portion between the firstand second gate structures.

Example 18 includes the subject matter of any one of Examples 14 through17, wherein the average thickness of the isolation structure centralportion between the first and second gate structures is in the range of1 to 5 nm.

Example 19 includes the subject matter of any one of Examples 14 through18, wherein the distance between the top surface of the first nanoribbonand the bottom surface of the second nanoribbon is in the range of 15 to40 nm.

Example 20 includes the subject matter of any one of Examples 14 through19, wherein the distance between the top surface of the first nanoribbonand the bottom surface of the second nanoribbon is in the range of 15 to30 nm.

Example 21 includes the subject matter of any one of Examples 14 through20, wherein the distance between the top surface of the first nanoribbonand the bottom surface of the second nanoribbon is in the range of 15 to20 nm.

Example 22 is a processor or memory comprising the integrated circuitstructure of any one of Examples 14 through 21.

Example 23 is an electronic system comprising the integrated circuitstructure of any of Examples 1 through 12 and 14 through 21, or theprocessor or memory of Example 13 or 22.

Example 24 is method of forming an integrated circuit structureincluding a stacked transistor architecture with a dielectric isolationlayer between top and bottom gate structures, the method comprising:removing dummy gate material to expose upper and lower channel regionsof the stacked transistor architecture, the upper and lower channelregions being part of a same multilayer fin structure; releasing, via aselective etch process, a first nanoribbon of the lower channel regionand a second nanoribbon of the upper channel region; forming a firstgate structure around each of the first and second nanoribbons of thelower and upper channel regions, respectively; recessing the first gatestructure to re-expose the upper channel region, including the secondnanoribbon; selectively and conformally depositing dielectric materialon a top surface of the first gate structure; depositing a mask on thedielectric material, and recessing the mask to a thickness in the range2 to 12 nm; removing unmasked portions of the dielectric material,thereby providing an isolation structure having a first end portion, asecond end portion, and a central portion between the first and secondend portions; removing the mask; and forming a second gate structurearound the second nanoribbon of the upper channel region, wherein atleast a portion of the second gate structure is on the central portionof the isolation structure and between the first and second end portionsof the isolation structure.

Example 25 includes the subject matter of Example 24, wherein thedielectric material of the isolation structure includes silicon, and oneor more of oxygen, carbon, and nitrogen.

Example 26 includes the subject matter of Example 24 or 25, whereinforming the first gate structure includes depositing a first high-k gatedielectric and then depositing a first gate electrode, and/or formingthe second gate structure includes depositing a second high-k gatedielectric and then depositing a second gate electrode.

Example 27 includes the subject matter of any one of Examples 24 through26, wherein prior to forming the first gate structure, the methodincludes depositing a passivation layer on the second nanoribbon of theupper channel region.

Example 28 includes the subject matter of any one of Examples 24 through27, wherein a largest thickness of the isolation structure centralportion between the first and second gate structures is within 10angstroms of the a smallest thickness of the isolation structure centralportion between the first and second gate structures, the averagethickness of the isolation structure central portion between the firstand second gate structures being in the range of 1 to 5 nm.

Example 29 includes the subject matter of any one of Examples 24 through28, wherein forming a first source region and a first drain region, eachadjacent to the first nanoribbon; and forming a second source region anda second drain region, each adjacent to the second nanoribbon; whereinthe first source and drain regions comprise one of a p-type or n-typedopant, and the second source and drain regions comprise the other ofthe p-type or n-type dopant.

Example 30 includes the subject matter of any one of Examples 24 through29, wherein a longest distance from a top surface of the firstnanoribbon to a bottom surface of the second nanoribbon is in the rangeof 15 to 50 nm.

The foregoing description of example embodiments of the presentdisclosure has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit the presentdisclosure to the precise forms disclosed. Many modifications andvariations are possible in light of this disclosure. It is intended thatthe scope of the present disclosure be limited not by this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. An integrated circuit structure, comprising: afirst semiconductor body; a second semiconductor body above the firstsemiconductor body, wherein the longest distance between an uppersurface of the first semiconductor body and a lower surface of thesecond semiconductor body is 50 nm or less, and wherein the first andsecond semiconductor bodies are part of a same fin structure; a firstgate structure on the first semiconductor body; a second gate structureon the second semiconductor body; and an isolation structure between thefirst and second gate structures and comprising dielectric material,wherein the isolation structure is on a top surface of the first gatestructure, the isolation structure including a central portion thatextends laterally between first and second end portions, the first andsecond end portions extending away from the central portion toward thesecond gate structure, such that at least a portion of the second gatestructure is on the central portion of the isolation structure andbetween the first and second end portions of the isolation structure. 2.The integrated circuit structure of claim 1, wherein the dielectricmaterial of the isolation structure includes silicon, and one or more ofoxygen, carbon, and nitrogen.
 3. The integrated circuit structure ofclaim 1, wherein the dielectric material of the isolation structureincludes silicon, oxygen, and carbon.
 4. The integrated circuitstructure of claim 1, wherein the first gate structure includes a firstgate electrode and a first gate dielectric between the first gateelectrode and the first semiconductor body, and/or the second gatestructure includes a second gate electrode and a second gate dielectricbetween the second gate electrode and the second semiconductor body. 5.The integrated circuit structure of claim 1, wherein the firstsemiconductor body includes a first nanoribbon, and the first gatestructure wraps around the nanoribbon, and wherein the secondsemiconductor body includes a second nanoribbon, and the second gatestructure wraps around the second nanoribbon, and wherein the longestdistance is a distance from a top surface of the first nanoribbon to abottom surface of the second nanoribbon and is in the range of 15 to 50nm.
 6. The integrated circuit structure of claim 1, wherein variation ofthe isolation structure central portion thickness between the first andsecond gate structures is less than 8 angstroms.
 7. The integratedcircuit structure of claim 1, wherein variation of the isolationstructure central portion thickness between the first and second gatestructures is less than 6 angstroms.
 8. The integrated circuit structureof claim 1, wherein variation of the isolation structure central portionthickness between the first and second gate structures is less than 4angstroms.
 9. The integrated circuit structure of claim 1, comprising: afirst source region and a first drain region, each adjacent to the firstsemiconductor body; and a second source region and a second drainregion, each adjacent to the second semiconductor body; wherein thefirst source and drain regions comprise one of a p-type or n-typedopant, and the second source and drain regions comprise the other ofthe p-type or n-type dopant.
 10. The integrated circuit structure ofclaim 1, wherein the longest distance between the upper surface of thefirst semiconductor body and the lower surface of the secondsemiconductor body is in the range of 15 to 40 nm.
 11. The integratedcircuit structure of claim 1, wherein the longest distance between theupper surface of the first semiconductor body and the lower surface ofthe second semiconductor body is in the range of 15 to 30 nm.
 12. Theintegrated circuit structure of claim 1, wherein the longest distancebetween the upper surface of the first semiconductor body and the lowersurface of the second semiconductor body is in the range of 15 to 20 nm.13. A processor or memory comprising the integrated circuit structure ofclaim
 1. 14. An integrated circuit structure, comprising: a firstnanoribbon comprising a first semiconductor material; a secondnanoribbon above the first nanoribbon and comprising the firstsemiconductor material, wherein the distance between a top surface ofthe first nanoribbon and a bottom surface of the second nanoribbon is inthe range of 15 to 50 nm, and wherein the first and second nanoribbonsare part of a same multilayer fin structure; a first gate structurearound the first nanoribbon, the first gate structure including a firstgate electrode and a first high-k gate dielectric between the first gateelectrode and the first nanoribbon; a second gate structure around thesecond nanoribbon, the second gate structure including a second gateelectrode and a second high-k gate dielectric between the second gateelectrode and the second nanoribbon; and an isolation structure betweenthe first and second gate structures and comprising dielectric material,wherein the isolation structure is on a top surface of the first gatestructure, and a bottom surface of the second gate structure is on a topsurface of the isolation structure, and wherein the isolation structureincludes a central portion that extends laterally between first andsecond end portions, the first and second end portions extending awayfrom the central portion toward the second gate structure for a distanceof 2 to 12 nm, such that at least a portion of the second gate structureis on the central portion of the isolation structure and between thefirst and second end portions of the isolation structure.
 15. Theintegrated circuit structure of claim 14, wherein the dielectricmaterial of the isolation structure includes silicon, oxygen, andcarbon.
 16. The integrated circuit structure of claim 14, wherein alargest thickness of the isolation structure central portion between thefirst and second gate structures is within 10 angstroms of a smallestthickness of the isolation structure central portion between the firstand second gate structures, and wherein the average thickness of theisolation structure central portion between the first and second gatestructures is in the range of 1 to 5 nm.
 17. An electronic systemcomprising the integrated circuit structure of claim
 14. 18. A method offorming an integrated circuit structure including a stacked transistorarchitecture with a dielectric isolation layer between top and bottomgate structures, the method comprising: removing dummy gate material toexpose upper and lower channel regions of the stacked transistorarchitecture, the upper and lower channel regions being part of a samemultilayer fin structure; releasing, via a selective etch process, afirst nanoribbon of the lower channel region and a second nanoribbon ofthe upper channel region; forming a first gate structure around each ofthe first and second nanoribbons of the lower and upper channel regions,respectively; recessing the first gate structure to re-expose the upperchannel region, including the second nanoribbon; selectively andconformally depositing dielectric material on a top surface of the firstgate structure; depositing a mask on the dielectric material, andrecessing the mask to a thickness in the range 2 to 12 nm; removingunmasked portions of the dielectric material, thereby providing anisolation structure having a first end portion, a second end portion,and a central portion between the first and second end portions;removing the mask; and forming a second gate structure around the secondnanoribbon of the upper channel region, wherein at least a portion ofthe second gate structure is on the central portion of the isolationstructure and between the first and second end portions of the isolationstructure.
 19. The method of claim 18, comprising: forming a firstsource region and a first drain region, each adjacent to the firstnanoribbon; and forming a second source region and a second drainregion, each adjacent to the second nanoribbon; wherein the first sourceand drain regions comprise one of a p-type or n-type dopant, and thesecond source and drain regions comprise the other of the p-type orn-type dopant.
 20. The method of claim 18, wherein a largest thicknessof the isolation structure central portion between the first and secondgate structures is within 10 angstroms of the a smallest thickness ofthe isolation structure central portion between the first and secondgate structures, the average thickness of the isolation structurecentral portion between the first and second gate structures being inthe range of 1 to 5 nm, and wherein a longest distance from a topsurface of the first nanoribbon to a bottom surface of the secondnanoribbon is in the range of 15 to 50 nm.